Cells use the genetic information contained in DNA to generate proteins, which carry out many of the processes of life. RNA is the intermediate molecule; it is transcribed from DNA, then edited, before being translated into proteins. Scientists have long sought to understand how all these molecules fit together when life first started. One prevailing theory is that life may have begun about 4 billion years ago not with DNA, but with RNA molecules. A new study has added some credence to that idea.
Researchers have now engineered an RNA molecule that is able to replicate, and like what happens in evolution, it can change and add complexity. The RNA encodes for an enzyme called a replicase, which can create copies of the molecule. RNA replication has been a challenge to develop. This may be the first concrete evidence that life can emerge from a simple set of molecules. In this study, the self-replicating RNA molecule diversified into five separate lineages. The work has been reported in Nature Communications.
"We found that the single RNA species evolved into a complex replication system: a replicator network comprising five types of RNAs with diverse interactions, supporting the plausibility of a long-envisioned evolutionary transition scenario," said first study author and Project Assistant Professor Ryo Mizuuchi of the University of Tokyo.
There is a concept called the 'competitive exclusion principle' in evolutionary biology, which suggests that if more than one species is competing for the same resource, they can't coexist. Thus, molecules also have to use different resources to sustain diversification, explained Mizuuchi. "They are just molecules, so we wondered if it were possible for nonliving chemical species to spontaneously develop such innovation."
At first, the researchers doubted "that such diverse RNAs could evolve and coexist," said Mizuuchi. This study showed otherwise, and may help us answer the question of how life first emerged on our planet. This work is just the beginning, added Mizuuchi. The system developed in this study will allow the researchers to investigate evolutionary processes at a new level of resolution.